A small irregular coccoid methanogenic bacterium (PA T ) was isolated from the hindgut of the cockroach Periplaneta americana. Fluorescence microscopy and transmission electron microscopy of the hindgut of P. americana suggest that the organism occurs abundantly in the microbiota attached to the hindgut wall. The strain produces methane by the reduction of methanol and methylated amines with molecular hydrogen. Acetate, coenzyme M, yeast extract, tryptic soy broth and vitamins are required for growth. The cells lack a rigid cell wall and lyse immediately in buffers of low ionic strength. Maximum rate of growth (specific growth rate, 022 h V1 ) occurs in a rich medium at 39 SC, at a pH range of 72-77 and at a salt concentration below 100 mM NaCl. Sequence analysis of the small-subunit rDNA indicates that strain PA T is related to the family Methanosarcinaceae but does not belong to any previously described genus. Therefore, it is proposed that strain PA T be classified in a new genus, related to the Methanosarcinaceae, as Methanomicrococcus blatticola (type strain PA T l DSM 13328 T ).